KR100351571B1 - Method of controlling dust - Google Patents

Abstract

By mixing the powdered material with polytetrafluoroethylene and subjecting the mixture to a compressive-shearing action at a temperature of about 20 to 200 ° C, thereby fibrillating the polytetrafluoroethylene to suppress dust of the powdered material. In the dust suppression method for powdered materials, the present method is an emulsifying stabilizer containing a hydrocarbon-based anionic surfactant of 1.0 wt% or more with respect to polytetrafluoroethylene, and having a specific gravity of 2.20 or less and an average particle diameter of 0.10-0.50 μ . A method for controlling dust of a powdery substance, characterized by using an aqueous emulsion of a homopolymer of fluoroethylene.

Description

Dust suppression method {METHOD OF CONTROLLING DUST}

Detailed description of the invention

Japanese Patent Application Laid-Open No. 52-32877 discloses a powdered material by mixing powdered material with PTFE, compressing and shearing the mixture at a temperature of 20 to 200 ° C, thereby fibrillating PTFE to suppress dust of the powdered material. Disclosed is a method for suppressing dust.

The PTFE disclosed therein is TEFLON ^? 6 or TEFLON ^? Homopolymer in the form of fine powder or emulsion of tetrafluoroethylene represented by 30 and also TEFLON ^? 6C or TEFLON ^? It includes a modified polymer in the form of fine powder or emulsion of tetrafluoroethylene represented by 64.

After that ^{"TEFLON? K-10" (} PTFE fine powder) and ^{"TEFLON? K-20" (} PTFE emulsion) has been developed, which are being released for vibration applications.

In the PTFE, fluctuations in the dustproof effect occur due to insufficient fibrillation, unsatisfactory strength of raw fibers, and non-uniform distribution of PTFE in powdery materials.

Particularly in the case of emulsion type dustproof agents, there is a problem related to the emulsion itself, such as precipitation and aggregation of PTFE colloidal particles caused by mechanical action during its transport, metering, and dilution, which causes clogging of pipes, pumps, orifices, etc. And a decrease in the concentration of PTFE in the emulsion, resulting in an incorrect mixing ratio of PTFE to powdery material.

Moreover, as a result of using a large amount of emulsion type dustproof agents for powdery materials such as fertilizers, soil stabilizers, and landfill materials such as coal ash, the surfactants used as emulsifying stabilizers may be contaminants such as groundwater, lakes and rivers.

It is an object of the present invention to provide a method for effectively suppressing dust of powdery materials using an aqueous emulsion of tetrafluoroethylene homopolymer, which is very stable and unlikely to be a contaminant of groundwater.

Disclosure of the Invention

Example of a method for suppressing dust of a powdery substance by mixing the powdery substance with PTFE, compressing and shearing the mixture at a temperature of 20 to 200 ° C, thereby fibrillating PTFE to suppress dust of the powdery substance According to the invention, the present method is an aqueous emulsion of a homopolymer of tetrafluoroethylene containing 1.0 wt% or more of a hydrocarbon-based anionic surfactant as PTFE, and having a specific gravity of 2.20 or less and an average particle diameter of 0.10-0.50 μ . It characterized in that to use.

Best way to carry out the invention

Although PTFE includes a so-called modified polymer that is a copolymer of tetrafluoroethylene and a so-called homopolymer of tetrafluoroethylene and up to 1% comonomer, PTFE useful in the present invention is a homopolymer. The anti-vibration agent using the aqueous emulsion of the modified PTFE polymer shows a lower dust-proofing effect than the dust-proofing effect of the present invention, and often requires an excess of 50% dust-proofing agent to show the same effect.

PTFE suitable for the present invention has an average particle diameter in the range of 0.10-0.50 µ , preferably 0.10-0.30 µ , and has a specific gravity of 2.20 or less, preferably 2.18 or less. Colloidal particles having an average particle diameter of less than 0.10 μ have an inferior dustproof effect, and particles larger than 0.50 μ cause an instability emulsion. PTFE with a specific gravity above 2.20 has an inferior dustproof effect.

The average particle diameter of the PTFE particles can be determined by the centrifugal sedimentation method. For the present invention, a centrifugal sedimentation particle size distribution analyzer (Shimazu Corp .; SA-CP4L) was used. Specific gravity was measured using agglomerated colloidal particles according to the method described in US Pat. No. 3,142,665.

The PTFE particles can be obtained by emulsion polymerization as described in US Pat. No. 2,559,752, wherein tetrafluoroethylene is used as an aqueous surfactant containing an anionic surfactant having a hydrophobic fluoroalkyl radical as a water soluble polymerization initiator and an emulsion stabilizer. The medium is filled under pressure to polymerize to form PTFE aqueous emulsion. However, because the PTFE aqueous emulsions so obtained are inferior in stability, they also require the addition of emulsifiers.

Emulsifying stabilizers used in the present invention are hydrocarbon-based anionic surfactants, which are caused by surfactants because they form insoluble or sparingly soluble salts in water by reacting with calcium, aluminum and iron, which are essential components of the soil. Avoid groundwater contamination. References are made to hydrocarbon-based anionic surfactants such as salts of higher fatty acids, salts of higher alcohol sulfate esters, salts of fatty oil sulfate esters, salts of aliphatic alcohol phosphate esters, salts of dibasic fatty acid ester sulfonic acids, salts of alkylarylsulfonic acids, and the like. have. Among them are poly (oxystyrene-alkylphenylether-ethylenesulfonic acid _having- (CH ₂ CH ₂ O) _1-6- and C _8-11 alkyl, alkylbenzenesulfonic acid having C _10-12 alkyl and C _8-10 alkyl The Na, K, Li and NH ₄ salts of the dialkylsulfosuccinic acid esters having exemplified are preferred as to provide a PTFE aqueous emulsion having high mechanical stability. The amount of emulsifier stabilizer to be added is at least 1.0 wt%, preferably 1.5-5 wt% of PTFE. An amount of less than 1.0 wt% provides an unsatisfactory stabilized aqueous PTFE emulsion, with an amount of more than 10 wt% being uneconomical.

Although the content of PTFE in the emulsion is not particularly limited, a low content is preferred for improved dispersion of PTFE into dust generating materials. On the other hand, a high content can reduce the transportation cost of the emulsion. So the content of PTFE is usually 10wt% or more, preferably 20-70wt%. Higher content is undesirable since it lowers emulsion stability. Thus, commercial dustproofers have a PTFE content of 20-70wt%, and the product is usually diluted with water to produce a PTFE content of less than 5wt% before mixing with the dust generating material.

The mechanical stability of an aqueous PTFE emulsion can be assessed by observing the rate of increase in the apparent size of the associated colloidal particles caused by the collision during the high speed agitation of the emulsion. And a portion of the agglomerated colloidal particles caused by the agitation adheres to the stir rotor and the walls of the vessel or forms a flock separated from the emulsion. Under the occurrence of this phenomenon, the emulsion is considered to have inferior stability despite the change in the size of the colloidal particles remaining in the emulsion.

In the present invention, the mechanical stability is determined by the rate of particle size increase measured according to the following procedure. Into a 60 mm inner diameter beaker is filled 200 ml of an emulsion having an average particle diameter of S ₁ .

An agitator (URTRA-TURRAX: manufactured by JANKE and KUNKEL GMBH and Co. KG) with a shaft attached to the generator is installed so that the shaft is 15 mm above the bottom of the beaker and 5 mm eccentric.

After rotating the rotor at 20,500 rpm for 5 minutes, the average particle diameter (S ₂ ) of the emulsion is measured.

The particle growth rate is calculated as follows:

% Increase in particle size = (S ₂ -S ₁ ) / S ₁ x100

Mechanical stability is evaluated as follows:

Good when "particle growth rate" is> 0%-<5%,

Usually when the "particle growth rate" is ≥5%-<10%,

Weak when the "particle growth rate" is ≥10%.

Furthermore, weakness is assessed when a large amount of aggregates are displayed by stirring.

Dust suppression rate is determined by the following procedure. From one end of a 34 cm high x 23 cm wide x 1.8 m long box air duct, use a blower to pass air at a rate of 0.25 m / sec. Through the 2 cm diameter outlet of the funnel installed above the outlet of the conduit, the dust-free lime is dropped at a constant rate (3-10 g / sec), and the lime accumulated on the 34 cm x 34 cm dish below the outlet is considered to be the amount of dust lime. The dust suppression rate is calculated as follows:

Dust Inhibition Rate (%) = Weight of Dust Lime / Weight of Falled Lime x 100

Test 1

Mix 18 ml of aqueous PTFE emulsion A, B, C, D, E, F, G or H mentioned in Table 1 and Table 2 with 800 ml of water and mix the mixture 20 kg of quicklime with a particle diameter of 5 mm or less. Sprayed on each. The quicklime mixed with PTFE emulsion was pressed and sheared for 2 minutes in a 50 liter plaster mixer, during which the temperature in the mixer increased due to the reaction between the quicklime and the water in the aqueous emulsion, generating water vapor Removed quite a bit.

Thus, a dustproof quicklime containing a small amount of slaked lime formed by the reaction between quicklime and moisture was obtained. The dust inhibition rate was measured for each of the quicklime samples thus obtained, and the results are shown in Tables 1 and 2. Each example using the aqueous PTFE emulsion of the present invention A, B, C or D has a higher dust than the dust suppression rate of the emulsion F having a specific gravity of more than 2.20 PTFE particles or the comparative example using emulsion G, an aqueous emulsion of modified PTFE. It was found to indicate inhibition rate. Moreover, the comparative example using the emulsion E containing 0.5 wt% of emulsion stabilizer was impossible to spray due to the aggregation of the emulsion.

Test 2

Portland cement was prepared by mixing cement clinker with an appropriate amount of gypsum and grinding the mixture in a finishing mill. The product had a particle size of 1.1% residue on a 88 μ sieve, a specific surface area of 3300 cm 2 / g and a temperature of 100-120 ° C. measured by the Blaine method. Portland cement at 100-120 ° C. from the finishing mill was charged to a twin-spindle paddle mixer (15 rpm) at a rate of 5 T / H with a volumetric continuous feeder.

At the same time each of the aqueous 30 wt% PTFE emulsions A, B, C, D or H mentioned in Tables 1 and 2 were fed into the metering pump at a rate of 16.7ks / H (5 kg / H of PTFE solids) to disperse and mix.

The PTFE was immediately fibrillated and distributed homogeneously into Portland cement to continuously produce a powder composition. During operation each emulsion A, B, C or D can be fed continuously for 200 hours, but emulsion H containing a non-ionic surfactant is agglomerated PTFE to cause clogging of the pump to remove aggregates. After 20 hours a break in operation was required.

Test 3

1000 ml of water were added to each 100 g of quicklime dusted by emulsions A, B, C, D or H used in Test 1, and stirred with a stirrer (heating initially) to prepare milk of lime. . The milk of lime was allowed to settle for 2 days and the supernatant was analyzed by liquid chromatography to detect emulsion stabilizers. As a result, an emulsion stabilizer of 0.2% content was detected only for emulsion H.

The present invention relates to a method for suppressing dust of a powdery substance using high dust-preventive polytetrafluoroethylene (hereinafter referred to as PTFE).

The dust suppression method according to the present invention shows an improved dustproofing efficiency for powdery materials and reduces the possibility of contamination of groundwater.

Claims (4)

By mixing the powdered material with polytetrafluoroethylene and subjecting the mixture to a compressive-shearing action at a temperature of about 20 to 200 ° C, thereby fibrillating the polytetrafluoroethylene to suppress dust of the powdered material. In the dust suppression method of powdered material, tetrafluoroethylene containing an anionic surfactant of 1.0 wt% or more with respect to polytetrafluoroethylene as an emulsifier and having a specific gravity of 2.20 or less and an average particle diameter of 0.10-0.50 μ . A method for suppressing dust of a powdery substance, wherein an aqueous emulsion of a homopolymer of is used. The method of claim 1, wherein the hydrocarbon-based anionic surfactant is Na, K, Li and NH of polyoxyethylene- alkylphenylether- ethylenesulfonic acid _with- (CH ₂ CH ₂ O) _1-6 -and C _8-11 alkyl. Dust suppression method of powdered material, characterized in that selected from the group consisting of _four salts. The method of claim 1, wherein the hydrocarbon-based anionic surfactant is selected from the group consisting of Na, K, Li and NH ₄ salts of alkylbenzenesulfonic acid having C _10-12 alkyl. The method of claim 1, wherein the hydrocarbon anionic surfactant is selected from the group consisting of Na, K, Li and NH ₄ salts of dialkylsulfosuccinic acid esters having C _9-10 alkyl. .